JPH0727127B2 - Optical system with reciprocal polarization rotator - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates generally to optical systems, such as fiber optic communication systems and optical mass storage devices, and more particularly to optical systems with an antireciprocal polarization rotator. Regarding

2. Technical Background Optical systems for information communication and information storage are well known and are now in a commercially important position. For example,
As schematically shown in FIG. 1, an optical communication system usually includes a semiconductor laser, which emits an optical signal.
For example, an information-carrying optical signal is sent to an optical fiber, which sends the optical signal to a photodetector. As schematically illustrated in FIG. 2, the optical mass storage device typically comprises an optical disc that can be or is being processed to store information. This information is encoded (through processing) on the disc as different optical properties, eg, different light reflectance regions. The disc is then read. That is, the information stored on the disc is the light source,
For example, by illuminating the disk with a semiconductor laser (usually through a beam splitter). next,
Light reflected from the disk is incident on the photodetector (ie,
It is reflected by the beam splitter. ). On the one hand, the light transmitted through the disc is sent to another photodetector.

Many optical systems include devices that rotate the polarization direction of linearly polarized light in the same direction, independent of its propagation direction. For example, the frequency and power intensity spectrum of light emitted by a semiconductor laser used in an optical system changes when reflected light is incident on the laser. Such a change is not desirable because it gives an error to the detection information.
Therefore, an attempt has been made to develop a device called an optical isolator that isolates a semiconductor laser from reflected light.
FIG. 3 shows an optical isolator based on the rotation of linearly polarized light, which is a bulk magnetic garnet material arranged between polarization and analyzers, such as bulk single crystal yttrium / iron / garnet (Y ₃ Fe). ₅ O ₁₂ , YIG)) material. This optical isolator operates at a wavelength of about 1.3 μm because the single crystal YIG is substantially light-transmitting (transmits at least 50% of incident light) in the infrared wavelength region (about 0.8 μm to about 6 μm). It has been proposed for use in optical fiber communication systems. When operating this isolator, magnetize YIG with a magnet (in the light propagation direction). The linearly polarized light emitted from the laser and passing through the polarizer is incident on the YIG material. Due to the effect of the net magnetic efficiency in the (magnetized) material, this linearly polarized light is subject to circular birefringence. (In a bulk material, for example, a bulk single crystal YIG, linearly polarized light is composed of right-handed and left-handed circularly polarized light components. Circular birefringence is the result of seeing different refractive indices of these two components. , Which means that one of the above components propagating in the material will be faster than the other.) As a result, the light remains linearly polarized, but its polarization direction is clockwise or as light propagates through the material. It will be continuously rotated in either the counterclockwise direction (as shown in FIG. 3). [This phenomenon is generally called the Faraday effect or magneto-optical rotation, and is described in, for example, the McGraw-Hill Science and Technology Dictionary, 5th Edition, 5th Edition.
Volume (McGraw-Hill, 1982) Page 314 (the McGraw Hil
l Encyclopedia on Science and Technology, 5th editi
on, Vol. 5 (McGraw Hill, 1982), P. 314). With proper sizing of the material, the light will be rotated (rotated) by, for example, 45 ° and will therefore be transmitted by the analyzer in the proper direction. The reflected light that passed through the analyzer is also incident on the YIG material and is rotated 45 ° in the same direction as the light that first passed through the material. Therefore, the reflected light after passing through the YIG material becomes 90 ° with respect to the light transmission direction of the polarizer, which prevents the light from entering the laser. (The linear polarization of the magnetized material propagating forward and backward in the same direction
The phenomenon of rotating by 45 ° (or an odd multiple of 45 °) is called antireciprocal magneto-optical rotation. Devices containing such materials are called reciprocal devices. ) A second type of device based on the rotation of linearly polarized light is a circulator. Such a device
For example, when used in an optical communication system, an optical signal from a semiconductor laser can be efficiently coupled to one end of an optical fiber, and a counterpropagating optical signal emitted from the same fiber end can be detected. FIG. 4 illustrates an example of such an optical circulator (having a structure suitable for effectively coupling light to the end of the optical fiber and extracting light therefrom). This circulator has a single-crystal YIG in a bulk state and further has a reflection device for detecting polarized light, like the above isolator. When operating this circulator, a magnet that magnetizes YIG in the light propagation direction is used. Linearly polarized light emitted from the end portion of the optical fiber, for example, light which is linearly polarized horizontally (as seen at the fourth position) is incident on the magnetized YIG. (This optical fiber is, for example, a polarization-maintaining fiber. On the one hand, a polarizer with an appropriate orientation is placed between the non-polarization-maintaining fiber and the YIG.) If the size of the YIG is chosen properly, the light will be , For example 45 ° (clockwise as seen from the fiber in FIG. 4) and sent to the detector by a polarization detection reflector. The linearly polarized light emitted by the laser, which has a direction of, for example, −45 ° (relative to this linearly polarized light emitted from the fiber), is magnetized by a polarization sensitive reflector YI
Reflected by G. This light after propagating through the YIG is 45 ° (4th
It is rotated (clockwise as seen from the fiber in the figure) and is therefore linearly polarized horizontally and enters the fiber.

Reciprocal optical rotators based on bulk materials, such as single crystal YIG isolators and circulators, are useful but coarse (usually 3mm x 3mm x 3mm in size) and have large magnetic fields (typically around 1000 Oersteds). (Oe) or more), it is more expensive (usually about 1000 dollars), and therefore unsuitable as a commercial product. On the one hand, thin film (thickness less than about 10 times the incident light wavelength) waveguide reciprocal device, for example a planar magnetized optical isolator or circulator, is a much more attractive device commercially. . For example, the use of thin film devices allows the use of guided optics (thus eliminating the need for a condenser lens omitted in FIGS. 1 and 2) and requires relatively small magnitudes of the applied magnetic field. (Less than about 100 Oe), and relatively cheaper. Moreover, the thin film device can be used as a constituent unit of an integrated optical device (an optical device having various functions and having two or more constituent components formed on the same substrate) used in an optical system. is there.

Although thin film reciprocal devices appear attractive, thin film waveguides experience linear birefringence. (For thin films, linearly polarized light can be represented as consisting of two orthogonal linearly polarized components.) In one of these components, the electric field of light (electromagnetic waves) is directed parallel to the thin film surface, It is called TM component. In the other component, the electric field is directed perpendicular to the thin film surface and is called the TE component. By linear birefringence is meant that the two components are combined with different indices of refraction, with the result that one of these components propagates through the film at a faster rate than the other. Regarding linear birefringence in thin film waveguides, see, for example, PK Tian, "Applied Optics", Volume 10, p. 2395, 1971 (PKTien, App.Oqt., Vo
l.10, P. 2395 (1971)). In this way, elliptical birefringence, that is, birefringence including both linearly polarized light components and circularly polarized light components, is received when propagating through a magnetized thin film. Therefore, the initially linearly polarized light will oscillately rotate. (The distance that light propagates when one vibration is completed is called the birefringence period P.)
As shown in the figure, the incident light is incident on the magnetized thin film at an angle of zero (with respect to the y-axis). The light propagating through the membrane is initially rotated at a relatively small angle, for example 3 ° clockwise. When it further propagates, it rotates -3 ° in the opposite direction, and when it propagates and reaches the distance P, it returns to the initial state (that is, it becomes parallel to the y axis). During this oscillating rotation, the polarization of light also continuously changes from linearly polarized light to elliptically polarized light and further to linearly polarized light. The amplitude of vibration is constant and small for most materials, for example 3 ° or 4 ° so that there is little or no net rotation. As already mentioned, the reciprocal device must undergo more rotation than is normally obtained with linearly birefringent materials, and the exiting light will be nearly linearly polarized, which will cause optical isolator detection. It must be possible to avoid, for example, loss of optical power at the photon. In this way, the linear birefringence device has the effect of eliminating their convenient use without compensation. Magnetized thin film optics that are conveniently used as optical switches or light modulators have been reported that compensate for linear birefringence effects. (PK Tian et al., "Optical Switching and Modulation in Magneto-Optical Waveguide Garnet Film")
Applied Theory Theory, Vol. 21, No. 8, October 15, 1972, Vol. 39
Pages 4 to 396 (“Switching And Modulation of Light in M
agnets-Optic Waveguide Garnet Films ", Applied Phys
ics Letters, Vol. 21, No. 8, October 15, 1972), and (Blank et al) Blank et al., U.S. Patent 3,764,195,1973.
See October 9, 2010. ) As shown in FIG. 6, this device comprises a magnetic garnet thin film epitaxially grown on a garnet substrate and a serpentine microcircuit formed on the upper surface of this garnet thin film.
The microcircuit is formed such that the direction of the current flowing therethrough is reversed every half birefringence period. In this way, the magnetization direction in the thin film (along the light propagation direction) is reversed every half of the birefringence period, which allows more rotation than normally obtained with linear birefringent materials. , The ellipticity of polarized light is not removed.

A device which receives linear birefringence and is used as a circulator or an isolator has also been reported. ("Faraday rotation in an optical fiber having high birefringence", "Applied Optics", Vol. 19, No. 6, March 15, 1980, pages 842 to 845, such as RHStolen). (“Faraday Rotation in Highly Birefringent Optica
l Fibers, "Applied Optics, Vol.19, No.6, March 15,198
0), and EHTurner et al., "Faraday Circulators or Isolators in Fibers," Optics, Vol.
Volume 7, Issue 1981, Pages 322-323 ("Fiber Faraday
Circulator or Isolator, "Optics Letters, Vol.6, No.
7, July 1981)) This device comprises a linear birefringent optical fiber and a plurality of spaced magnets (in the direction of light propagation) that magnetize a series of fiber regions. The polarity of each magnet is opposite to that of the preceding magnet and the spacing of the one-way magnets is half the fiber birefringence period of the fiber. The number of these spaced magnets, and thus the corresponding number of spaced magnetized fiber regions, is empirically selected (relative to the particular fiber) and therefore exits the last magnetized fiber region. The resulting light is elliptically polarized, and the light intensities along the two birefringent axes of the fiber are equal. In operation, elliptically polarized light is converted to linearly polarized light by propagating light through the relatively long (about 6 birefringence period), unmagnetized, heated portion of the fiber extending from the last magnetized fiber region. The amount of heating is empirically determined. On the one hand, the above-mentioned light is made to pass through an external compensating plate, and this compensating plate also converts elliptically polarized light into linearly polarized light. The setting of this compensator (necessary to obtain linearly polarized light) is also made empirically. From the above, rotation more than that normally obtained with linear birefringent material,
It allows the elimination of the ellipticity of the polarization and thus its use as a reciprocal device. However, researchers who are engaged in the development of optical systems, although not yet successful, have considered a linear birefringent optical isolator / circulator device that conveniently (rather than empirically) converts elliptically polarized light into linearly polarized light. Is the current situation.

SUMMARY OF THE INVENTION The present invention provides an optical system with a linearly birefringent, nearly reciprocal device, such as an optical isolator or circulator. This device increases the amplitude of the vibration received by the incident light (either rectified or unrectified) to give a net rotation (in linear birefringent material) equal to approximately 45 ° within a finite distance. More than what is usually obtained). Furthermore, the device converts elliptically polarized light into linearly polarized light without the use of heat or other empirical means. Further, the conversion is accomplished by device components incorporated within the device.

The above-mentioned device used in the optical system of the present invention provides the elliptical birefringence (in operation) in the light propagation direction together with the sign and / or the magnitude of either the linear component or the circular component of the elliptical birefringence which changes for each material region. It has a series of material regions shown. (For example, in the case of a thin film, the sign of the linear component and /
Or the change in magnitude is TE and TM without magnetization.
It means a change in the sign and / or the magnitude of the velocity difference of the components. The change in the sign and / or the magnitude of the circular component means the change in the direction and / or the magnitude of the Faraday rotation (optical rotation) when there is no linear birefringence. ) Except one respective regions (device) has a length substantially equal to _^1/2 birefringence period of the region (in the propagation direction of light). However, in contrast to prior such devices, the first or last material region is substantially anti-reciprocal (antireciprocal) operation is obtained if having a length approximately equal to _^1/4 birefringence period Not too much. If the length of the last region of _^1/4 period, only when the polarization direction of the first _^1/2 incident on the periodic area linear polarization substantially parallel to one of the linear birefringence axis of the device, approximately Reciprocal action is achieved. The length of the first region is ^_1/4
During the period, almost reciprocal motion is obtained only when the polarization direction of the light incident on this region is polarized so as to be approximately 45 ° with respect to one of the linear birefringence axes of the device. .

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described with reference to the accompanying drawings.

1 and 2 are a schematic diagram of a conventional optical fiber communication system and a schematic diagram of a conventional optical mass storage device, respectively, and FIG. 3 is a conventional bulk single crystal magnetic garnet optical isolator. FIG. 4 is a schematic view of an optical system equipped with the above, FIG. 4 is a schematic view of an optical system equipped with a conventional bulk single crystal magnetic garnet optical circulator, and FIG. 5 is a magnetized linear birefringent medium. FIG. 6 shows a state of oscillatory rotation of light propagating in the light. FIG. 6 shows a known device using a thin film magnetic garnet material useful as an optical switch or a modulator. 9 is a schematic view of three embodiments of the optical system according to the present invention, and FIGS. 10 to 13 show four embodiments of the optical isolator used in the optical system according to the present invention. Figure Shows an embodiment of the optical circulator used in the optical system according to the present invention, and FIG. 15 shows an optical circulator obtained by using the embodiment of the reciprocal device used in the optical system according to the present invention. FIG. 16 shows the degree of rotation of the polarization direction (optical rotation) as a function of the propagation distance of, and FIG. 16 shows a known two-layer device for reducing unwanted guided modes. 17 to 21 show an embodiment of a reciprocal device according to the present invention.

DETAILED DESCRIPTION The present invention includes an optical system, such as a fiber optic communication system or an optical mass storage device. The optical system provides error-free detection information and / or effectively couples light to the end of an optical fiber without the use of bulk or bulk optical isolators or bulk optical circulators.

An optical system according to the present invention, as shown in FIGS.
Reference numeral 10 is an anti-reciprocal device, for example, an optical isolator or an optical circulator, and is constituted by a component 30 using a linear birefringent material. If the component 30 is, for example, an optical isolator, then the system 10 is generally further comprised of the components shown in FIGS. That is, this component comprises a light source 20 such as a semiconductor laser, a component 50 on which light emitted from this light source 20 passes through the optical isolator 30 and a photodetector 80. This component 50
Has an optical fiber 60, for example, as shown in FIG. One side, as shown in FIG.
Includes a beam splitter 65 and an optical disc 70.

For example, if the system element 30 is an optical circulator, the system 10 will typically be a light source 20 as shown in FIG.
And a photodetector 25 and an optical fiber 50. The light emitted from the light source 20 is coupled to one end of the fiber 50 via the circulator 30. Circulator 30 above
Is also used to couple the light emitted from the end of the fiber into the detector 25. Generally, other photodetectors and / or light sources (with or without circulator 30)
Is located on the opposite side of the fiber. (In the present embodiment, the optical fiber 50 is considered to be, for example, a polarization maintaining fiber. If not, the system further includes a polarizer between the fiber 50 and the optical circulator.) System Component When 30 is an optical isolator (10th ~
See Example 4 in FIG. ), The isolator has a material 40 between the polarizer 32 and the analyzer 48. Polarized optical fibers are used for the polarizer 32 and the analyzer 48, for example. When a polarizer is inconvenient, it can be immediately replaced by a region of metal (not shown), eg aluminum, gold, titanium, etc., which is then one of the materials 40 (where light passes). It is arranged next to the light source 20 on the section. Such a metal region absorbs reflected light having a polarization direction intersecting with the polarization direction of the light emitted from the light source 20 (propagating forward). The thickness of this metallic region is preferably between about 0.01 μm and about 10 μm. A thickness of less than about 0.01 μm is not desirable because it reduces the absorption of the thin film obtained. A thickness of about 10 μm or more is not very desirable, if not excluded, because the resulting thin film does not give greater absorbance than thin ones and it takes longer to manufacture.

In operation, the analyzer 48 and material 40 are used to adjust the polarization direction (backpropagation) of the reflected light perpendicular to the polarizer, thus eliminating light transmission to the light source 20. When the light source 20 is largely unaffected by such vertically aligned light, the polarizer 32 (or metal region) is not needed.

When the system component 30 is an optical circulator, this circulator comprises material 40 (see the embodiment shown in Figure 14). Furthermore, the circulator comprises means 90 for directing the two light beams of different polarizations to different optical paths, for example known optical devices such as polarization sensitive reflectors or rutile plate (s). .

The material 40 used in an anti-reciprocal device, such as an isolator or circulator, has a series of material regions 44 through which forward and backward propagating light passes. Each of these regions is light transmissive (transmits at least 50% of the incident light), and at least some of these regions are magnetic (ie, magnetizable). It is not necessary that these material regions have the same thickness and composition, but generally, if they are easily manufactured, the thickness and composition are easy to be uniform. In addition, the material area 44
Is preferably manufactured as a continuous thin film (having a thickness less than about 10 times the wavelength of the incident light), but thick films are also useful,
It is not excluded. Such thin and thick films are subject to linear birefringence, so that the magnetic region exhibits elliptical birefringence (in the direction of light propagation) when magnetized. Material region 44, when formed as a thin film, preferably has a thickness in the range of about 0.1 μm to about 100 μm. A thin film having a thickness of about 0.1 μm or less is relatively unfavorable as an optical waveguide. When the thickness is about 100 μm or more, the light passing through such a thick film undesirably spreads (in the thickness direction), which makes it difficult to directly couple this light to other optical components, which is also undesirable.

To overcome the effect of such linear birefringence,
That is, incident linearly polarized light at an angle (or
In order to rotate elliptically polarized light into linearly polarized light by rotating it through (an odd multiple of 45 °), the reciprocal device 30 must satisfy two conditions. First, the sign and / or magnitude of the linear component or the sign and / or magnitude of the circular component of the elliptical birefringence exhibited by the (magnetized) region 44 should vary from region to region. Second, the beginning, or each of the material region except for the last region should have substantially equal light propagation direction length _^1/2 birefringence period of the region (P). (The birefringence period for each region is that one complete oscillation (osci
given as the distance to complete. ) One,
The first region or last region, should have a length substantially equal to _^1/4 birefringence period of any region of this like. It should be emphasized here that in the absence of such an initial or final region, the outgoing light cannot be redirected 45 ° (relative to the incident light) and will generally not be elliptically polarized. . (The birefringence period P in each of the regions 44 is not necessarily the same because this period depends on, for example, the composition of the region, the degree of magnetization of the region, and the wavelength of incident light. , The birefringence period of each region will generally be measured for the specific conditions in which the region operates.A useful measurement for this is, for example, “LPE-Growth” by K. Ando et al. -Induced Optical Birefringence in Type Bilayer Iron Garnet Film "
"Applied Physics" Vol.22, No.10, October 1983, L618-L62
0 (“Growth Induced Optical Birefringence in LPE−
Grown Bi-Based Iron Garnet Felms, "Japanese J. Appl
Phys., Vol. 22, No. 10, October 1983).

FIGS. 10 to 14 show an embodiment of the optical isolator / circulator 30 in consideration of the above two conditions. For example, in the embodiment shown in FIG. 10, the sign of the circular component of elliptical birefringence changes from region to region, ie the direction of magnetization (indicated by the single headed arrow) changes from region to region. (Length P / 2
The non-magnetized regions of P, or the regions where the magnetization is oriented perpendicular to the light propagation direction and the length P / 2 is interposed between the magnetized regions are not excluded. The existence of such a region only affects the direction of rotation. That is, in some cases such regions only change, for example, a + 45 ° rotation to a −45 ° rotation. In the embodiment of FIG. 11, it is the size of the circular component that varies from region to region (the magnetizations of the second, fourth, and sixth regions of FIG. 11 are parallel to the light propagation direction). Since they are aligned, they have a non-zero circular component, but the first, third, fifth, and seventh regions have zero circular components because their magnetizations are aligned perpendicular to the light propagation direction.) The sign of the linear component of the birefringence changes alternately in the embodiment shown in FIG. 12 (this will be described in detail below). In the case of the embodiment shown in FIG. It is the magnitude of the linear component. One way to change the magnitude of the linear component is to form alternating material regions of different thickness. ) One way, again
As shown in FIG. 13, all regions are initially manufactured to a uniform thickness, and then a material region 46 having a lower index of refraction than that of the region 44 below is provided by conventional selective deposition ( deposition)
And / or etching techniques are applied over every other region 44. ) In general, the number of regions of length approximately equal to P / 2 required to obtain a rotation approximately equal to 45 ° (or an odd multiple of 45 °) is empirically determined (eg, control samples with different numbers of regions). By measuring the rotation above that normally achieved with linearly birefringent materials). To achieve the object of the present invention, the rotation angle is approximately 45 ° or an odd multiple thereof if the intensity of the light from the light source 20 is at least 10 times or more the intensity of the reflected light transmitted through the polarizer 20. Must be equal. Furthermore, and in order to achieve the object of the present invention, the material regions are selected such that the number of regions produces a rotation of, for example, 45 °, and the intensity of the light from the light source 20 is also polarized. If the intensity of the reflected light transmitted through the child 32 is at least 10 times or more, the length should be approximately equal to P / 2 and P / 4.

When the composition and thickness of the material region 44 are basically the same, and the rotation of the polarized light is obtained by reversing the magnetization direction, a region having a length of P / 2 necessary to realize the rotation of 45 ° is formed. Number N
Is the relational expression It has been found that can be sufficiently approximated by. Where F
Indicates the (uniform) magnitude of the specific Faraday rotation (rotational frequency per unit length) in the material region. One,
Δβ indicates the (uniform) magnitude of linear birefringence in the above region (ie, Note that n _TE and n _TE are the effective refractive index seen by the TM wave and the effective refractive index seen by the TE wave, respectively, and λ is the wavelength of the light in vacuum. When it is desirable to use a number (N) of material regions (for a particular wavelength of light λ) that does not satisfy equation (1), this number is still usable, and equation (1) still , F and / or Δβ can be satisfied (for a particular light wavelength λ). For example, F can be changed immediately by changing the magnetization component in the light propagation direction. Such changes can be made, for example, by rotating the magnetic field used to align the magnetization directions so that the magnetization is not parallel to the light propagation direction (and thus reduces the magnetization component of the light propagation direction). Can be realized immediately. On the one hand, Δβ is one or more of a smaller index of refraction than that of this region 44, by varying (uniformly) the thickness of the material region 44 or above and / or below the region 44. It can be changed immediately by forming a material layer of This material may be, for example, silicon dioxide, silicon nitride, gadolinium gallium garnet.

Once the number of regions needed to obtain a 45 ° rotation has been determined (empirically or by using, for example, equation (1),
A rotation equal to the desired multiple of ° is obtained immediately by using a multiple of the (original) number of regions. However, the order of each successive region set should be the reverse of the previous set. For example, if three P / 2 and P / 4 regions (eg, with magnetization reversal) provide 45 ° rotation, an additional P / 4
The region (when there is no reversal of magnetization between the two P / 4 regions) and the following three additional P / 2 regions (indicating reversal of magnetization) give a rotation of 90 °. Furthermore, 3 with P / 4 region
Addition of two P / 2 regions gives a rotation of 135 °.

If either one of the two conditions is fulfilled, the device according to the invention immediately gives a nearly anti-reciprocal motion (whether this gives a rotation of 45 ° or an odd multiple of 45 °). (Regardless of). The first condition is that when the P / 4 region is the last material region, the incident light should be incident on the first material region substantially parallel to one of the two axes of the linear birefringence of this device. Given by that. (The linear birefringence axis refers to the two directions of the device that can be immediately determined empirically in the absence of magnetization.) For example, if linearly polarized light is incident on a non-magnetized control sample of the device in any direction, the linear birefringence axis Is the axis in the direction that does not change the polarization. ) The second condition is that when the P / 4 region is the first material region, the incident light is at an angle approximately equal to 45 ° with respect to either of the linear birefringence axes (ie + 45 ° or −45 °). It should be incident on the above region. (For the purposes of the present invention, incident light is approximately parallel to one of the birefringent axes, or 45 ° to one of the birefringent axes.
Are oriented so that they are approximately equal to each other, so that nearly reciprocal motion is achieved if the two conditions are met. First, select the number and length of the material area and select 45 °.
Or it should give an odd number of rotations of 45 °. next,
The intensity of the light from the light source 20 must be at least 10 times higher than the intensity of the reflected light transmitted through the polarizer 32. A large number of (magnetic) materials can be used in the device of the invention, the practicality of which is partly given by the transparency to incident light. For example, YIG is infrared light (wavelength range is about
It is a useful material that almost transmits light between 0.8 μm and about 6 μm). Iron borate (FeBO ₃ ) is also useful and is substantially transparent to light in the wavelength range of about 0.5 μm to about 3 μm. Furthermore, cadmium-manganese-telluride is also useful,
It is almost transparent to light having a wavelength range of about 0.6 μm to about 5 μm. Other useful materials are, for example, "Magnetic Optical Materials" by WJ Tabor ("M
agneto-Optic Materials ") [F.T. Aletsch and E.O. Schultz-" Laser Handbook "edited by DuBois, North Holland Publishing Amsterdam, 1
972 (Laser Handbook, edited by FTArecchi and E.
O.Schultz-DuBois, North Holland Publishing Compan
y, Amsterdam, 1972)].

Many ways are possible to create regions of material that provide (linear) birefringence of varying (sign). For example, the magnetic material iron borate (FeBO ₃ ) provides both circular birefringence (when magnetized) and crystalline (linear) birefringence. (FeBO ₃ of 2
The two crystallographic axes are labeled a and b in FIG. In this way, by stacking opposite crystal parts so that they are adjacent to each other (as shown in FIG. 12), a magnetic material having alternating (sign) linear birefringent regions is obtained.
(For this method, incorporated by reference,
See Kurtzig et al., U.S. Pat. No. 3,617,942, issued Nov. 2, 1971. ) A method of forming regions of material with alternating (sign) circular birefringence consists of applying opposite magnetic fields to adjacent magnetic regions. This is achieved, for example, by forming a serpentine microcircuit on the surface of a magnetic material and passing an electric current through it (see Blank et al., Dated October 9, 1973, cited herein). As described in Japanese Patent No. 3,764,195.).

For example, there are other methods that are immediately applicable to thin film magnetic garnet waveguides, such as thin film YIG waveguides, to form material regions with alternating circular birefringence, which provide a change in sublattice magnetization. For example, the structure of YIG (Y ₃ Fe ₅ O ₁₂ ) is such that 3 out of 5 iron atoms of each molecule are arranged at tetrahedral lattice sites, and the remaining 2 atoms are arranged at octahedral sites. Given. Furthermore, the three magnetic efficiencies of tetrahedral sites (related to tetrahedral iron atoms) are parallel to each other, but antiparallel to the two magnetic efficiencies of octahedral sites. Thus, in the presence of an external magnetic field, the (main) tetrahedral efficiency is parallel to the applied magnetic field and the uni-octahedral efficiency is antiparallel to the magnetic field. Importantly, Faraday rotation (optical rotation)
It is the direction of octahedral efficiency that mainly determines the direction of.

The YIG alternating (sign) circular birefringence regions are formed, for example, by reducing the magnitude of the tetrahedral efficiency in selected material regions to a point where the octahedral efficiency in these regions becomes dominant. Thus, in the presence of a magnetic field, the (currently dominant) octahedral efficiency in the selected region is aligned parallel to the applied magnetic field, but in the non-selected regions (where the tetrahedral efficiency is still dominant). The efficiency is anti-parallel to the magnetic field, and therefore the selected and non-selected regions are given Faraday rotations of opposite sign.

The reduction of the tetrahedral efficiency of the selected YIG material region can be readily realized by replacing (at least partially) the iron atoms located at the tetrahedral sites with non-magnetic ions, such as gallium or aluminum or germanium ions. Such substitution may be accomplished, for example, by first forming, or growing, non-magnetic ions of octagonal and tetrahedral lattice sites in a YIG material, and then non-magnetic ions (as described below) in the octahedral lattice of selected regions. It is realized by moving from the site to the tetrahedral lattice site.

The transfer of non-magnetic ions between the lattice sites described above is readily accomplished by the procedure described in Le Craw et al., US Pat. No. 3,845,477, dated October 29, 1974, which is incorporated herein by reference. Here, a thin film doped with non-magnetic ions
YIG is epitaxially grown, for example, on a gadolinium gallium garnet (GGG) substrate 45 (see FIG. 7) by conventional methods. The doped YIG thin film should have a composition close to the "compensation point" (composition with zero net magnetic efficiency), but the net tetrahedral efficiency still predominates over the net octahedral efficiency. Must be one. Thus, when the non-magnetic ion is, for example, potassium, its composition is preferably 1.05 ≦ x ≦ 1.45 and Y ₃ Ga
Given as _x Fe _5-x O ₁₂ . Values of x less than about 1.05
The tetrahedron efficiency obtained remains undesired after the treatments described below, ie the octahedron efficiency is undesired because there is no predominance. An x value of about 1.45 or higher is also undesirable because the octahedral efficiency obtained is predominant, and therefore there is no place where the tetrahedral efficiency dominates.

Selective replacement of tetrahedrally arranged iron atoms in selected material regions with, for example, gallium ions is accomplished by first forming a Si region with a thickness in the range of about 1000Å to about 5000Å over each of the selected material regions. Will be realized. This Si
The regions are formed by a conventional selective deposition procedure or by forming a Si layer overlying the entire top surface of the YIG thin film and then removing selected Si layer portions by conventional etching methods. Next, this thin film of YIG has a temperature range of about 4
From 00 ℃ in a nitrogen atmosphere of about 800 ℃ about _^1/2 hours to about 2
Annealed for 4 hours. About 400 ° C or less and about
_^1/2 hours or less annealing time, since the transfer of gallium ions do not give almost or entirely undesirable. about
Annealing temperatures above 800 ° C. and annealing times above about 24 hours are undesirable because all regions, including those not coated with Si, undergo similar amounts of gallium ion transfer.
After cooling to room temperature (over the desired time period), the area not covered by Si remains essentially unchanged, but the silicon-covered area undergoes the transfer of gallium ions from the octahedral to the tetrahedral lattice sites. become.

There is a new method of forming regions of material with mutual (sign) circular birefringence in the thin film YIG, which uses thin films that are sufficiently doped with non-magnetic ions to form a uniform octahedral dominant region. is there. In this method, the non-magnetic ions are then moved from the tetrahedrons of the selected material region to the octahedral lattice sites, so that these regions are dominated by the tetrahedra. So also in the presence of a magnetic field,
The octahedral powers (moments) of the selected material regions are themselves aligned antiparallel to the magnetic field, and the octahedral powers (moments) of the one-way non-selected regions are themselves aligned parallel to the magnetic field.

The YIG film used in this method, as already noted,
Close to the "compensation point", but with a composition that provides octahedral dominance. When gallium is a non-magnetic ion, the composition of the thin film is given by Y ₃ Ga _z Fe _{5 -z} O ₁₂ with 1.1 ≦ z ≦ 1.5. Values of z below about 1.1 are undesirable because the resulting film has a dominant tetrahedral (rather than a dominant octahedron) efficiency. On the one hand, z- values above about 1.5 are not desirable, as the octahedral efficiency obtained is still dominant after the treatments given below.

Transfer of gallium ions from tetrahedral sites to octahedral sites in selected material regions heats these selected material regions to a temperature of at least 1200 ° C. for a duration equal to at least 1 microsecond and then It is realized by cooling these regions to room temperature over a time width of about 10 seconds or less, preferably about 0.1 seconds or less. About 1200
Heating temperatures of less than or equal to 0 ° C. and heating times of less than about 1 microsecond are undesirable because they result in undesirably small numbers of gallium ions being transferred from the tetrahedral sites to the octahedral sites. On the other hand, a cooling time of about 10 seconds or more causes undesirably large amounts of gallium ions to move from the tetrahedral site to the octahedral site and then back to the tetrahedral site, predominantly affecting the sublattice. It is not desirable because it is left as it is. The heating and cooling procedure above is
Immediately at selected material regions by selective scanning with a laser, eg, a continuous wave (CW) argon ion laser.

The above method of modifying sublattice magnetization assumes that the YIG film (doped with non-magnetic ions) has an easy axis parallel to the top surface of the film (and thus aligned with the direction of light propagation). . However, arsenic grown thin films typically
It shows growth-induced anisotropy and magnetostriction, for example, compressive anisotropy. The former brings an easy axis of magnetization perpendicular to the film plane,
The latter gives an easy axis of magnetization parallel to the film plane. When these growth-induced anisotropies are very large and therefore the easy axis of magnetization is perpendicular to the film surface, these anisotropies must be eliminated. In most cases, this is a conventional annealing method (eg AJ Kurzich and FB Hagedorn).
"Anisotropy of non-cubic magnets in bulk and thin film garnets", IEEE Transmagnetics, Vol. 7, 1971, 473.
Page (“Noncubic Magnetic Anisotropies in Bulk and T
hin Film Garnets, "IEEE Trans.Magnetism, Vol.MAG7, P.
473). ) Can be realized immediately.

As is known, doping of YIG films with bismuth (which replaces Y) significantly increases the Faraday rotation (optical rotation), but also enhances the growth-induced anisotropy. Furthermore, these enhanced growth-induced anisotropies cannot be annealed from the material because the required temperature is very high (above about 1300 ° C.) and therefore the YIG film is significantly damaged or destroyed. Has long been considered. (For example,
P. Hansen et al., "Magnetic and Magneto-Optical Properties of Bismuth-Substituted Gadolinium Iron Garnet Films," Physics Research B, Vol. 27, No. 7, April 1, 1983 ("Magnetic
and Magneto-Optical Propertics of Bismutn-Substi
tuted Gadolinium Iron Garnet Films ", Physical Revie
w B, Vol. 27, No. 7, April 1, 1983) pp. 4375-4383. ).

It has been found that the growth-induced anisotropy of bismuth-doped YIG films can be immediately annealed from the film without damaging the film by doping the film with Ca (replacing Y) before annealing. Preferably, the composition of the bismuth and calcium doped film is given by _{Y 3-ab Bi a Ca b} Fe 5-c X c O 12. Here, 0.2 ≦ a ≦ 2.0, 0.001 ≦ b ≦ 0.1, and x is
For example, it represents a non-magnetic ion such as gallium, and c represents the amount of X per unit formulation. Furthermore, the annealing temperature is preferably between about 900 ° C. to about 1300 ° C., annealing time is preferably between about _^1/4 hour to about 24 hours. Values of a below about 0.2 are undesirable because the resulting Faraday rotation (optical rotation) is reduced rather than increased. Values of a greater than or equal to about 2.0 are undesirable because growth of thin films of high optical quality is difficult. B value of less than about 0.001 is
This is undesirable because the required annealing temperature is undesirably high. Values of b greater than about 0.1 are obtained when the resulting membrane is, for example,
It is not preferable because it has an undesirably low transmittance for infrared light. Annealing temperature less than about 900 ℃, and about ¹ /
An annealing time of ₄ hours or less is not preferable because the growth-induced anisotropy of the obtained film is undesirably large. About 13
Annealing temperatures of 00 ° C. and above and annealing times of about 24 hours and above are undesirable because the resulting film is susceptible to decomposition.

For example, many methods have been reported for forming a material region having a magnetization aligned in the YIG in parallel and perpendicular to the light propagation direction. One such method is, for example,
"LP by EMGyorgy" etc.
Position control of uniaxial anisotropy in E-bubble garnet film "
"Theory of Applied Materials" Vol. 25, No. 3, 1974, 167-168
Page (“Local Control of Uniaxial Anisotropy In LPE
Bubble Garnet Films ", Applied Physics Letters, Vol.2
5, No. 3, (1974)).

Optical waveguide devices, such as thin films or optical fibers, anti-reciprocal polarization rotators (APR _s ) are typically designed to rotate only one or several selected guided modes.
(When an electromagnetic wave is approximated as a light beam, the guided mode shown here is, for example, a light beam that is totally internally reflected in the thin film of the APR or in the optical fiber core. The performance of such APR _s is thus undesired due to the thin film or optical fiber core having a higher refractive index than the surrounding medium, such as the substrate supporting the thin film or the cladding surrounding the optical fiber. mode (i.e., correct the APR _s is the guided mode that is not rotated) is thought to be enhanced gradually as the number of decreases. This is important to the operation of the APR _s is based on the assumption that only the waveguide mode.

Previous studies to be formed waveguide APR _s with reduced number of the guided mode (by others) is the recognition that may be reduced by the number of guided modes reduce one of two Barameta It was based. That is, guided wave AP
If the thickness of R is kept constant, reducing the refractive index difference between the APR and the underlying or surrounding medium, the critical angle (rays are totally internally reflected, APR and below, Alternatively, the maximum angle (measured from the interface with the surrounding medium) is reduced, thus reducing the possible number of guided modes.
On the other hand, if Δn is constant, for example, if the thickness of APR is reduced, the diameter of the thin film or APR optical fiber core increases the angular spacing between adjacent mode rays, which again reduces the number of guided modes. .

For example, in the case of a YIG film formed on a GGG substrate, YI
Relatively large refractive index difference between G and GGG (The refractive index of YIG is GGG
About 10% higher than that. ) Increases the number of modes guided by the YIG film. Therefore, to achieve single mode operation, the YIG film thickness should be reduced to about 1 μm or less. Such a very thin YIG film is formed immediately using, for example, the conventional liquid phase epitaxy (LPE) method, but such a thin film is used, for example, to align a light source, for example a semiconductor laser, to such a film, Therefore, it is often inconvenient because it is difficult to couple light into such films. Moreover, these ultrathin films often introduce undesirably large amounts of linear birefringence into the APR.

To achieve single-mode operation without the use of ultrathin films, the device was prefabricated (otherwise) and formed on a GGG substrate (as shown in Figure 16) YIG (composition). Are modified). (A Shibukawa (A.Sh
See "Applied Optics, 20, page 2444 (1981)", "Applied Optics", No. 20, page 2444 (1981). ) The bottom YIG layer has a slightly smaller refractive index than the top YIG layer (because of a slightly different composition) but higher than that of the GGG substrate (see the refractive index profile shown in Figure 16). Have. The thickness of the upper YIG layer is a few microns.
Single-mode waveguiding is realized in the upper YIG layer because the index difference between the upper and lower YIG layers is much smaller than that between the upper (or lower) YIG layer and GGG.

It has been found (by the inventors) that reducing the number of guided modes in a guided APR (to the mode for which the APR was designed) is not in itself sufficient in many cases to improve the performance of the APR. Has been done. For example, the waveguide APR is one of the optical isolators.
In the case of the component (see FIG. 10), the guided polarization rotation (rotation) mode (or multiple modes) is transmitted to the optical fiber, for example, by the analyzer of the optical isolator. Any of the transmitted light is passed through the analyzer by the optical fiber and APR
If reflected back to, the light is reflected at the interface between the guided APR, eg, the YIG layer and the underlying material layer, such as the second YIG layer (of low index) or the GGG substrate, at an angle greater than or equal to the critical angle. It seems that there are many things to illuminate. Therefore, this reflected light is neither guided by APR nor rotated properly. However, in most cases, the reflected light will be guided by a waveguide having the APR and the underlying substrate material. this,
Back-propagating light guided by the substrate and the APR often exits the substrate and illuminates the light source shielded by the optical isolator, thus reducing the effectiveness of the optical isolator.

Furthermore, for example, the effectiveness of the waveguide APR _s for use in an optical isolator or circulator, if two conditions are met, it has been found that significantly increased. First,
The number of APR _s by waveguided mode (the actual and the same degree) to those correctly rotated by APR _s should be reduced. Second, and just as importantly,
The substrate material underneath the APR, for example the substrate supporting the waveguiding film, or the cladding surrounding the waveguide core of the optical fiber, is the light guided by the substrate and the APR by at least a factor of 10 over the length of the APR. Should contain materials that reduce the electromagnetic energy of.

The first condition is, for example, a relatively small thickness (thickness selected to reduce the number of unwanted guided modes).
Satisfied by forming an APR. (This appropriate thickness is empirically determined by using various thickness control samples.) On the one hand, the refractive index difference between the APR and the medium below or surrounding it is reduced. This is because, for example, the substrate 130 below has a lower refractive index than that of region 10.
An area (or areas) of material larger than
APR over 0, eg waveguiding region 100 (see FIG. 7)
It is realized by forming. The index difference between the regions 100 and 110 required to guide the desired number of modes (both of which are assumed to have a uniform index as shown in FIG. 17). Δn is, for example, empirically determined (using control samples of different refractive index). One,
The Δn required to obtain the guided wave up to the maximum − mode (m = 0,1,2, ...) is It is sufficiently well approximated by the requirement. Where n ₁₀₀ and n ₁₁₀
Indicates the refractive index of the regions 100 and 110, respectively, and t indicates the waveguide region.
The thickness is 100, and λ ₀ indicates the wavelength of guided light (in vacuum). (For the above equation,
RGHunsperfger, "Integrated Optics, Theory and Technology," Springa Publishing, Berlin, 1982.
Year, page 37 (Integrated Optics: Theory and Technolog
y (Springer-Berlag, Berlin, 1982), page 37). ) The second condition is, for example, the material under the guided APR, eg
Satisfied if the underlying material (see FIG. 17) such as substrate material or region 110 absorbs modes not limited to APR. The absorbing material, eg, the inherently absorbing substrate material or absorbing dopant added to the substrate material should have an absorption coefficient t (t is the wavelength) at least 10 times greater than that of the APR material. Further, the absorbing material must be non-emissive (non-radiational) at that wavelength (to protect the light source from re-emitted light). Preferably, the absorptive material is well separated from the APR to avoid an undesirably large reduction in guided mode strength, which reduces the guided mode electromagnetic energy by about 50% over the length of the APR. Must be done. (The extinction field of the guided mode, that is, the exponential decay part of the electric field related to the guided light, contains a considerable amount of energy and often exists beyond the APR range.) In this case,
Suitable intervals are generally empirically determined. (Materials that scatter more than absorb light are less desirable because the scattered light can, for example, hit the light source to be shielded.) The APR100 shown in FIG. (B
i) formed in the doped layer (as described above), the substrate 130
In the case of GGG, the first condition is satisfied for a Bi-doped YIG layer in which the region 110 has a refractive index smaller than that of the region 100 (but larger than that of the GGG substrate 130). this is,
For example, it is realized by reducing the amount of Bi in the area 110. Such a decrease is caused by increasing the growth temperature.
Alternatively, this is accomplished immediately by reducing the spin rate during LPE growth in region 110, which forms the same melt as that used for region 100. On the other hand, the region 110 is grown from a different melt and the concentration of Bi contained in the constituent is reduced.

To achieve the second condition, praseodymium (Pr)
Alternatively, absorptive dopants such as germanium or cobalt or nickel, which have different absorption spectra, are incorporated (via the initial melt) into the Bi-doped YIG layer 110. (For example, the absorption spectrum of Rr shows absorption peaks at wavelengths of 1.48 μm and 1.54 μm, but shows relatively low absorption at 1.51 μm.) For example, if Pr is used as an absorbing dopant, the amount of Pr is About 0 per unit of formula.
It is between 05 and about 2 atoms. Amounts less than about 0.05 are not preferred because they have undesirably low absorption. Quantities above about 2 are undesirable because the resulting layers have large lattice constants making it difficult, if not impossible, to achieve good epitaxial growth on GGG substrates. (When using a substrate with a larger lattice constant, the amount of Pr can be up to about 3 atoms per unit of equation.) The thickness of the upper YIG region 100 is between about 1 μm and about 100 μm. Is preferred. A thickness of about 1 μm or less is not excluded, but it is not preferable because it is often difficult to couple light to such a thin film and the linear birefringence of the thin film is often undesirably large. . About 100
A thickness of μm or more is not excluded, but since light propagating through such a thick film diffuses undesirably in the thickness direction, it becomes difficult to directly couple the light to other optical components.
Not desirable. Moreover, such thick films are difficult to grow epitaxially.

The thickness of the lower YIG region 110 is between about 0.01 μm and about 100 μm. Such a thin film has a thickness of about 0.01 μm or less.
This is undesirable because it absorbs undesirably small amounts of light guided by the two YIG regions. A thickness of about 100 μm or more is not desirable because it is difficult to grow such a thick film by the epitaxial method.

According to the preferred embodiment of the invention shown in FIG. 18, APR1
The absorption of the eliminable field associated with the modes guided by 00 causes the two material regions 115 and 120 between the APR 100 and the substrate 130.
Can be avoided or can be significantly reduced. Here, it is the region 120 that contains the absorbing material, while the region 115 (which does not contain any strong absorbing material) is the region of the erasable field associated with the modes guided by the APR.
120 is formed thick enough to avoid absorption.
As shown in FIG. 18, in order to obtain an optical waveguide in the APR 100 (total internal reflection), the region 115 and the APR 100 have a smaller refractive index. However, in order to avoid total internal reflection at the interface between regions 115 and 120, and thus avoid unwanted modes, the refractive index of region 120 is configured to be greater than or equal to that of region 115.

If the regions 100, 115, and 120 are, for example, Bi-doped YIG, then the required change in refractive index is achieved by varying the amount of Bi as described above. In addition, absorbing dopants such as Pr are incorporated into region 120 (via the initial melt). Pr
The range of the amount of is given as above for the above reasons.

The thickness of region 100 extends over the above range for the above reasons.

Region 115 has a thickness of between about 0.1 μm and about 100 μm.
A thickness of about 0.1 μm or less is undesirable because such thin films include an undesirably small portion of the erasable field associated with the modes guided by region 100. About 100
A thickness of μm or more is not desirable because such a thick film is difficult to grow by the epitaxial method.

The thickness of region 120 extends over the above range relative to region 110 for the reasons described above.

In a variation of the preferred embodiment shown in FIG. 19,
APR region 100 is functionally similar to regions 115 and 120 and has two material regions 125 and 135 on top. The material area 125 is
It does not contain a strongly absorbing material, but has a lower refractive index than that of the APR region 100, but higher than that of the surrounding atmosphere. Therefore, the linear birefringence in the APR region is reduced. Area 1
35 contains a strongly absorbing material and has a refractive index equal to or higher than that of region 125 to avoid total internal reflection at the boundary of regions 125 and 135.

All of the above-described embodiments of the present invention, including those shown in FIGS. 17-19, include regions of different material, each region having an essentially uniform composition and an essentially constant refractive index along its thickness. In addition, there is (and is assumed to be) a refractive index discontinuity at the interface between different regions. However, since the present invention is immediately realized by using a device in which the optical waveguide has a graded refractive index, that is, a refractive index that changes smoothly, it is not necessarily limited to a device having the above discontinuity. It is not something that will be done. For example, FIG. 20 shows an embodiment of the present invention, which has a graded refractive index profile and
It has a single material region 140 that is functionally equivalent to the two regions 100 and 110 shown. Optical waveguides of one or more selected modes are achieved utilizing the local optical waveguide maximum 150 (described below) of the refractive index profile of region 140 (see FIG. 20). Absorption of modes not guided by the local optical waveguide maximum is achieved, for example, by incorporating an absorbing dopant in at least a portion of the region 140 below the optical waveguide maximum.

FIG. 21 shows still another embodiment of the present invention, which has a graded refractive index profile and has the structure shown in FIG.
It has a single material region that is functionally equivalent to the two regions 110, 115, and 120. The guided wave of one or more selected modes is a locally guided maximum of 170 (first
(See Figure 21). The second local guided maximum 180 separated from the first local guided maximum 170 by the local minimum 175 operates to prevent unwanted modes. The absorption of modes not guided by the local guided maximum 170 described above, for example, absorbs the absorbing dopant in at least a portion of the region 160 that lies below the local minimum 175 and extends across the local maximum 180. It is realized by incorporating.

As described above, the existence of the maximum local optical waveguide of the refractive index distribution is indispensable for the waveguide of one or more modes. For the purposes of the present invention, the concept of local optical waveguide maxima is not limited to graded index profiles, but can be applied to any profile, including discontinuous profiles. That is, and in order to realize the object of the present invention, the refractive index profile has a local guided maximum provided that two conditions are satisfied.
First, after performing Fourier analysis of the refractive index distribution,
_The curve defined by the sum of the Fourier components excluding wavelength components smaller than ₀ (wavelength of the fire to be guided in vacuum) should have a local maximum. Second, this local maximum is (at least on the curve above) at least 0.001% above the height of the two points at least 0.02λ ₀ to either side of it.
It should have a large height (amplitude).

(Heights of less than 0.001% are possible, but such small heights provide optical waveguides that are undesirably small, ie, the extinguishable field of the guided mode is undesirably out of the waveguiding region. It is generally undesirable because it extends far apart.) For example, if the above Fourier analysis is performed on the discontinuous distributions shown in Figures 17 and 18, the corresponding Fourier components (less than 0.05λ ₀ The curves defined by the sum (excluding the wavelength component) will be very similar to the refractive index profile shown in Figures 20 and 21, respectively. The local maxima of these curves are the local optical waveguide maxima if the magnitude of the discontinuous change in the index of refraction of the original distribution is greater than 0.001% of the smaller index of refraction. It becomes a value.

Example 1 Magnetic film _{Y 3-ab Bi a Ca b} Fe 5-c Ga c O 12 gadolinium gallium garnet by a conventional liquid phase epitaxy method (GG
G) was grown on the (111) plane of the substrate. However, a is about 0.
5, b is about 0.03, c is about 1.3, and the film thickness is 2.8 μm. The growth temperature was about 900 ° C. This film had a growth-induced anisotropy that gave an easy axis of magnetization perpendicular to the film surface. Furthermore, this film also provided an easy axis of magnetization parallel to the film surface in the absence of growth-induced anisotropy, and also had compression anisotropy induced in the presence of Bi (which replaces Y) and Ca. . (Bi also increases the Faraday rotation in the film.) The GGG substrate supporting this film was placed between the pole pieces of the magnet, and the film was magnetized by a saturation magnetic field of 2000 Oe (aligned perpendicular to the film surface. To form a net efficiency. Next, the light was passed through a monochromator to generate light having a wavelength of 1.5 μm, which was made to enter the film surface perpendicularly. "Physics of Magnetic Garnets" edited by A. Paoletti North Holland 19
78 years (Physics of Magnetic Garnets, edited by A.Paol
When the Faraday rotation angle (optical rotation) received by 1.5 μm light is measured by the conventional method described in the chapter by JFDillon, Jr. of etti (North Holland, 1978), it is 140 degrees. / cm, and the sign of rotation corresponds to the octahedral sublattice dominance of the magnetization.

The growth-induced anisotropy of this film was removed by first annealing the film in a nitrogen atmosphere at about 1000 ° C for about 17 hours (giving an easy axis of magnetization parallel to the film surface). The membrane was then gradually cooled to room temperature (about 23 ° C) over about 17 hours.

The annealed film was magnetized by a small bar magnet aligned parallel to the film surface, which generated a saturation field of about 100 Oe. (The net efficiency is parallel to the film plane.). Burleigh Instruments Company of Fish, New York
linear polarized infrared light (wavelength is 1.45 μm) from a KCl: T2 ⁽⁰⁾ color center laser (tunable at 1.4 μm to 1.6 μm ⁾ purchased from ers, New York), Rutile prism (Codewell, NJ) Optics for optical equipment company for research
Membranes) through the Research Corporation of Caldwell, New Jersey). (Some modes that can be coupled to the film were the TM ₀ mode used here.) The rotation (optical rotation) that light receives when propagating through the film is until the minimum value of the transmitted light intensity is obtained (film The analyzer (located next to the output end of the membrane) was rotated relative to the polarizer (located next to the input end of the membrane) and measured. This procedure was repeated, shifting the coupling prisms along the length of the membrane. The rotation (optical rotation) of the obtained polarized light is plotted in FIG. 15 (a) as a function of the propagation distance of light. From this plot, which showed rotation oscillating from about + 4 ° to about -4 °, the birefringence period of the film was determined to be 1.84 mm.

CW with optical output focused by a lens with a focal length of 20 cm
A (continuous wave) argon ion laser was used to irradiate the laser annealed region of the film (thus also forming an inverted sublattice magnetized region). Annealing sets the laser power to 0.85 watts (about 10% below the film damaging threshold),
The film is 2 cm / sec against the laser, and the laser (r
ater) made a pattern and moved. Several 0.92 mm wide bands (half the birefringence period) were annealed and the annealed bands were separated by 0.92 mm wide unannealed bands. 0 adjacent to the polished edge of the membrane.
The 46 mm wide (1/4 of birefringence period) band was left unannealed. The obtained laser-annealed region appeared darker than the non-annealed region.

To bleach this darkened laser annealed area,
Approximately 1 in an atmosphere of N ₂ (85% by volume) and H ₂ O (15%) at 350 ° C
Heated for hours.

Linearly polarized light from the color center laser was recombined through the rutile prism into the bleached laser annealed film. The resulting rotation of the light (optical rotation) as a function of the prism's distance from the polishing edge of the film (the distance traveled by the light) is plotted in FIG. 15 (b). As is clear from the figure, the rotation increased monotonically with distance. (I.e., receiving the amplitude of vibrations of the light was increased according to the distance.) Further, also after 5 _^1/2 birefringence period and 1/4 birefringence period propagation (total distance 5.06Mm), the light is rotated + 45 ° , Became linearly polarized light.

To verify the reciprocity of this light rotation, + 45 ° polarized light (and counter-propagating) was coupled to the polishing edge of the film. This light 1/4 birefringence of the film period and 5 ^_1/2
It was found to have a + 90 ° orientation after propagating in the birefringent period length region.

Example 2 Three iron / garnet films were grown on the (111) plane of a GGG substrate by the conventional liquid phase epitaxy method. The upper magneto-optically active film was grown at a temperature of 950 ° C, and Y _{2 ・ 5} Ri _{0 ・ 5} Fe _{3 ・ 6} G
It had a nominal composition of a _1.4 C ₁₂ . This composition was selected so that the above-mentioned laser annealing method could give periodic inversion to the magnetization method. A small amount of Ca (about 0.2 atom or less per unit formula) is also incorporated into the upper film to lower the light absorption, and further, to provide oxygen vacancies that facilitate removal of the growth-induced uniaxial magnetic anisotropy by high temperature furnace annealing. I chose

An intermediate garnet film was grown from the same melt used for the top film, but the growth temperature was increased by 15 ° C. Therefore,
This film grows more slowly than the top film and has less Bi
Was incorporated into the film (about 0.1 less Ri per unit of formula), so the refractive index was slightly lower than the top film.

The nominal composition of the bottom garnet film is Y _1.7 Bi _0.5 Pr _0.3 Lu _0.5 Fe
_{It was 3.6} Ga _1.4 O ₁₂ . This Pr is added to match the lattice of the GGG substrate.

The refractive indices of the three films were evaluated (from top to bottom) as 2.17, 2.16, and 2.18 (at a wavelength of 1.5 μm). These evaluations were made on the basis of measurements of the refractive index of three corresponding single films, these measurements being made using the conventional prism coupling method.

The thicknesses of the above three kinds of garnet films (on the GGG substrate) were measured by a conventional interferometry method (using visible light at an incident angle of 45 °). These thicknesses (from top to bottom) are 3.5μm, 4.4μ
m, and 5.9 μm.

The guided modes of the three film structures were investigated by coupling infrared light into this structure through a rutile prism at a distance of 8 mm from the edge of this structure. The light from this edge is an infrared detection TV camera (Electrophysics Corporation of Nutey, Ne.
w Jersey) and model No. 7290). 1.4
A KCl: T1 ⁽⁰⁾ color center laser (purchased from Burleigh Instruments Company of Fisher, NY ⁾ tunable from μm to 1.6 μm was used as the infrared light source. Incident angle of laser light is about 3 ° to about 25
To 45 ° (measured from the direction perpendicular to the hypotenuse surface of the 45 ° -45 ° -90 ° prism), various TEs are added to the structure of the three types of film
The mode was made incident. The wavelength of light was also changed from 1.51 μm, which is a wavelength at which the lower Pr-containing film is sufficiently transparent, to 1.48 μm, and to 1.54 μm, which is a wavelength at which the lower film is sufficiently absorbing.

At 1.51 μm, 17 TE modes were made incident on the structures of the three types of films, and then emitted from them. 1.48 μm and 1.
At 51 μm, only the TE ₀ mode intensity was basically unaffected. The other 16 TEs emitted from the above structure
The intensity of each of the modes was reduced by at least a factor of 100.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location G02F 1/095 (72) Inventor Wolf, Raymond USA 07974 New Jersey, New Providence, Walker Drive 21 (56) Reference JP-A-58-190904 (JP, A) Thin Solid Films, vol. 114, no. 1/2, 1984 P.I. 187 −219

Claims (14)

[Claims] 1. An electromagnetic radiation source, and a component that is in optical communication with the electromagnetic radiation source and serves to transmit or reflect at least a portion of the electromagnetic radiation emitted by the electromagnetic radiation source. An optical system comprising an apparatus including a polarization rotator having substantially reciprocal characteristics capable of optically communicating with the electromagnetic radiation source and the component, the apparatus including the polarization rotator. A material having a refractive index profile with a first local optical guiding maximum located inside the polarization rotator, and during operation of the optical system traversing the device containing the polarization rotator but by the polarization rotator. An optical system having means for reducing the electromagnetic energy of at least a portion of the unguided electromagnetic radiation. 2. The optical system of claim 1, wherein the refractive index profile has a second local optical waveguide maximum within the device but outside the polarization rotator. 3. The optical system of claim 1, wherein the means comprises a material capable of absorbing electromagnetic energy. 4. The optical system of claim 3, wherein the device has first and second regions of material, the first local optical waveguide maximum is located within the first region, and The second material region is an optical system including an absorbing material capable of absorbing the electromagnetic energy. 5. The optical system of claim 2, wherein the means comprises a material capable of absorbing electromagnetic radiation. 6. The optical system according to claim 5, wherein the device comprises first, second and third material regions.
An optical system in which the optical waveguide maximum is located within the first region, the second optical waveguide maximum is located within the third region, and wherein the third region comprises the absorbing material. 7. The optical system of claim 1, wherein the material comprises yttrium, iron and oxygen. 8. The optical system of claim 7, wherein the material further comprises bismuth. 9. The optical system of claim 1, wherein the device comprises an optical isolator. 10. The optical system according to claim 1, wherein:
The apparatus is an optical system having an optical circulator. 11. The optical system according to claim 1, wherein:
An optical system further comprising a photodetector for detecting at least a portion of the electromagnetic radiation transmitted or reflected by said component. 12. The optical system according to claim 1, wherein:
An optical system in which the radiation source comprises a semiconductor laser. 13. The optical system according to claim 1, wherein:
An optical system in which the component comprises an optical fiber. 14. The optical system according to claim 1, wherein:
An optical system in which the component comprises an optical disc.